The .NET 5.0 release is composed of many improvements and features. This issue lists the "epics" that are part of the release (for dotnet/runtime). Beyond these epics are many "features" in this release that are not listed here, because they are not truly epics. An epic is a collection of features that together form a step-function level improvement in .NET, and typically requires the epic owner (a single developer or a small team) to go on a journey to satisfy the epic goals. Such a journey can require taking great personal risk or fighting dragons, but it's all worth it to make .NET better.
This list will be filled out over the course of the release. Team members working on epics are encouraged to edit this issue directly to add their epic. The order of the epics is arbitrary (like epics should be grouped together). A small set of these 5.0 epics may be enabling early (but partial) support for .NET 6.0 scenarios.
In short, no. The longer version is that there are two variants of Mono now, the one in dotnet/runtime that is the future of Mono (and currently only used for web assembly) and the the one in mono/mono that is used for everything else. Xamarin use cases will move to using the Mono in dotnet/runtime in 6.0. For the most part, Mono investments are focused on functional parity with CoreCLR and to improve the specific workloads that the Mono runtime is used for.